1. Field of Invention
The present invention relates to separation of dry powders, more particularly it relates to a centrifugal separator for continuous separation of dry powders.
At present, several methods are utilized for dry separation of powders including: air separation, vibration separation using batteries of sieves, and vibro-gravitational separation. In air separation systems, separation is realized by air jets, which remove fine particles out of powder flow and transfer them to a hopper, and heavy particles, which are not carried out by an air jet, fall into another hopper.
2. Description of Related Art
U.S. Pat. No. 5,934,483 to KOLACZ discloses an apparatus of the forced air vortex type for classification of particulate material into a fine portion and a coarse portion, the apparatus comprises a truncated cone shaped upper section having a separating wheel rotating about a substantially vertical axis, a vertically arranged inlet pipe for supplying a particulate material dispersed in an air flow, a conical feed distributor having a tip end directed downwards and arranged concentrically with the inlet pipe and the separating wheel, and a spiral shaped outlet for removal of classified fine material dispersed in air, and a substantially truncated cone shaped lower section, the upper section of which exhibit a secondary air inlet arranged tangentially to the circumference of the lower housing to supply secondary air in a direction concurrently with the direction of rotation of the separating wheel and a second outlet for classified coarse particulate material.
U.S. Pat. No. 4,869,786 to HANKE discloses a process and an air classifier for the separation of classifying material into coarse material and fine material. Known air classifiers suffer from considerable deficiencies with regards to the throughput and the separation efficiency. To avoid this, the device provides for the performance of a separate reclassification, which takes place in the same way as the pre-classification, whilst incorporating mechanical centrifugal rejection of coarse material particles, particularly through the impact ledges of a centrifuge basket.
U.S. Pat. No. 3,941,687 to PETERSON discloses a solids separation system designed for pneumatic separation of pieces of scrap particularly metallic scrap, into light and heavy fractions. The mixture of pieces of scrap is fed into an enclosed separation vessel wherein they fall by gravity into a horizontally directed stream of air blown into and across the separator vessel, whereby the heaviest pieces fall through the air stream into a heavy solids hopper and the lighter materials are carried downstream by the force of the horizontal air stream into a second hopper. A gas outlet port is provided at the top of the vessel thereby imparting an upward velocity vector to the gas. The horizontal velocity of the gas being reduced by expansion, light metal pieces fall out of the influence of the gas stream into the light solids hopper. Means are provided for adjusting the air flow path from the first into the second hopper comprising a pivoted angularly disposed baffle plate defining the rear wall of the first hopper, the surface of which plate also serves to direct solids intercepted thereby into the first hopper.
These methods are energy-consuming due to the necessity of continuous maintenance of air flows. Considerable air volumes become saturated with dust and require special air-cleaning equipment, which makes the facility awkward and expensive.
Separation using sieves has proven to be cheaper and ecologically cleaner. For example, U.S. Pat. No. 3,932,442 to SALMON discloses a process for screening materials as a function of particle size differences by feeding the materials onto one side of a substantially planar screen and vibrating the screen by producing a translational screen oscillation in directions normal to the screen plane and a torsional screen oscillation about an axis normal to the screen plane so that each point of the screen moves in a helical path. Screened material is collected at the other side of the screen and screened retentate is transported by the torsional screen oscillation to an exit port at a location spaced from the axis of torsional oscillation. The process is particularly applicable to shipboard or other mobile use, since the spring stiffness provides good structural support under tilt or side acceleration conditions.
This method is efficient for medium particle sizes in the powder where di greater than 50 xcexcm. However, at smaller particle sizes, the sieves are soon clogged up. The result is that the process efficiency abruptly decreases. Additionally, elongated particles with one of cross-sections corresponding to the mesh size of the sieve are undesirably allowed pass through the sieves.
Vibro-gravitational separation consists in a motion of particles of different sizes, densities or shapes under the action of vibration along different paths over an inclined concave. Sometimes numerous holes are made in the concave for the passage of compressed air supply, in order to increase the amplitude of particle jumps. This method has proved to be rather efficient for separating seeds and coarse-grain powders. However, its efficiency for powders with a medium particle size below I 00 pm is rather low.
The facility or device suggested in the application PCT/US 98/15797 and International Publication Number WO99/0747, the disclosures of which are expressly incorporated by reference in their entirety herein may be employed as a starting point for the system of the present invention. A separator proposed in this application operates cyclically. The powder is fed to the center of horizontal rotating disk, which spreads it along the entire Internal wall of a rotating cup. Dry powder is separated into two fractions on the internal wall of a rotating cup under the action of friction force and centrifugal force on each particle. Larger particles are allowed to pass over the upper edge of the cup, whereas smaller ones remain on the cup wall. However, to make particles fall down from the cup wall, it is necessary to stop the cup. After it stops, the action of centrifugal force on the particles is stopped, and they fall down into a respective hopper. In this state the facility is ready for the next separation cycle. The efficiency of such a separator has proven to be low, because a large share of operation time is spent on unproductive stops of an inertial cup. Moreover, due to multiple starts and stops, the service life of the engine or motor is shortened, and especially important, the power consumed per unit volume of separated powder is high because an electric engine consumes 2-3-fold amount of energy at the start than in the constant operation mode. Accordingly, improvement is still desired.
The present invention therefore provides a centrifugal separator for dry separation of powders having a high efficiency and a low power consumption due to its continuous operation. In other words, in the proposed separator the feeding of powder to be separated and the removal of coarse and fine powder fractions after separation take place simultaneously and continuously.
Powder separation occurs on a wall of a cavity of a rotating body. The body rotates around a vertical axis and has a centrally symmetrical cavity open from above and from below. The cavity symmetry axis coincides with the body rotation axis, and the cavity surface is a surface of revolution with circular upper and lower edge""s of this cavity, the diameter of the upper circumference being greater that the diameter of the lower circumference.
Powder is fed to a certain zone which is designated a feeding zone and which is positoned adjacent to a lower portion of the cavity surface. The length of this zone is designed to be much less (at least by an order of magnitude) than the length of a separation zone, with the length of the separation zone being approximately 1s. The length (in meters) of the separation zone is determined by the relationship 1sxe2x89xa71gxc3x97V/Vg, where 1g is the distance (in meters) between the lower edge of the feeding zone to the upper edge of the cavity surface along the generatrix of the surface of revolution, V is the linear velocity (in meters/second) of the upper edge of cavity surface, and Vg is the velocity (in meters/second) of the coarse powder fraction motion upwards along the generatrix of the surface of revolution.
Each material has its own characteristics, friction coefficient and density. Based upon these characteristics, separation is attainable with the invention. The velocity V depends on the material characteristics of the bowl, such as roughness, diameter, and shape. Thus in the case of separating fly ash, the following data correspond to the following bowl characteristics: the diameter of the upper edge of the bowl is 0.4 meters; the angle of the bowl surface is 40 degrees relative to the vertical bowl axis; and the surface roughness of the bowl surface is 2-3 microns, where 1 micron equals 10xe2x88x926 meters.
The diameter of course fraction particles can be designated as di greater than d, where d is the diameter of particles (in microns) according to which particles are separated into two fractions. After the separation zone, in the sense of the body rotation, is located the discharge zone, where a discharge facility or discharge device discharges the powder particles remaining on the cavity surface. Preferably, this device is arranged along the entire generatrix of the surface of revolution.
Separation proceeds as follows. The powder falls on a rotating surface of a cavity having a certain roughness (for example, a roughness of 2-3 microns is adequate for separating fly ash and graphite in a manner depicted in FIGS. 10 and 11). Since the resultant of all the forces acting on powder particles is different for large and small particles, the larger particles move upward and, during the passage of the separation zone from the feeding zone to the discharge zone, pass over the upper edge of the cavity surface and fall into one of the hoppers. The smaller particles remain on the cavity surface until they reach the discharge device, which discharges them into a respective hopper.
A further increase in the facility efficiency can be achieved by arranging several feeding zones and, respectively, separation zones and discharge zones along the cavity surface. Here one of the fractions which is obtained in one of the separation zones can be fed to another separation zone, which will improve the separation quality.
Moreover, powder can be fed to the feeding zone by an appropriately oriented pipe having a nozzle or by utilizing a plurality of rotating disks or rings, or else by a conveyer. These various rotating disks or rings can have a rotation axis which either does or does not coincide with the cavity rotation axis. Further, they can be driven by the same drive as the body or have an independent drive, each of which is independently controllable. Additionally, these disks or rings can be located in a plane perpendicular to the cavity rotation axis, or in some other plane. Moreover, they may be located in the same plane or one under another.
In many of these embodiments, the powder is fed by a pipe to the periphery of the rotating disk or ring and thrown into the feeding zone under the action of the centrifugal force.
One or more discharge devices may be in the form of a flat or round brush adjoining the rotating cavity. The brushes can be adjustably fixed or movable in longitudinal or transverse direction, or may be adapted to rotate around their axes. The discharge device can comprise one brush or several brushes located at various distances form one another. The discharge device can even represent a flexible elastic strip with one of end faces adjoining the cavity surface. Moreover, the discharge device also can represent a pipe with a suction nozzle at the end, with the nozzle being arranged along the generatrix of the surface of revolution, and rarefaction is created in the pipe and in the nozzle. Air flow sucked in by the nozzle tears powder particles off the cavity surface in the discharge zone and directs them into the nozzle and further, by the pipe, into a hopper.
According to one aspect of the invention, there is provided a system for dry separation of powders into at least two fractions including a powder to be separated and a separator comprising a hollow body rotating around a vertical axis, the cavity of the body being often from above and from below and the surface of the cavity represents a surface of revolution with the central axis coinciding the rotation axis of the body, the upper edge of the cavity having a greater diameter than the lower edge, a system controlling the rotation of the body, at least one feeder continuously feeding dry powder into a feeding zone adjacent to the cavity surface near its lower edge, the length of the zone being at least an order of magnitude less than the circumference of the cavity surface in its lower portion, at least one discharge device continuously discharging powder from the cavity surface, which represents a prolonged body arranged along the entire length of the generatrix (the generatrix being a generating line for a body of revolution. In the case of a cone, it is a straight line) of this surface adjoining the surface and located immediately in front of the feeding zone aligned with the rotation of the cavity surface, and at least two hoppers, one of which is intended for powder fraction consisting of powder particles passing over the upper edge of the cavity surface in the course of separation, and the second is intended for powder fraction remaining on the cavity surface until the discharging device discharges it from the rotating surface into the hopper. The slope of the generatrix of the surface of revolution with respect to the vertical may be within the limits from approximately 10xc2x0 to 45xc2x0, and the roughness of the cavity surface may be within approximately 0.01d to 0.2d, where d is the diameter of particles, by which the powder is separated into fractions so that particles with diameters dixe2x89xa6d are found in one fraction, and particles with diameters dixe2x89xa7dxe2x80x94in another.
Moreover n pairs of feeder/discharging device may be uniformly arranged over the cavity surface so that the following relationship is valid: Lxe2x89xa7n(1f+1s+1u), where L is the circumference length of the lower edge of the cavity surface, 1f is the feeding zone length, 1s is the separation zone length, 1u is the discharging zone length, the separation zone length being 1sxe2x89xa71gxc3x97V/Vg, where 1g is the distance between the lower edge of the feeding zone to the upper edge of the cavity surface, V is the linear velocity of the upper edge of cavity surface, Vg is the mean velocity of the rise of coarse powder fraction particles along the generatrix of the surface of revolution.
The feeder may consist of a rotating disk and a pipe for feeding powder to this disk, the disk being disposed inside the cavity of the rotating body in the plane perpendicular to the rotation axis of the rotating body, and the outlet of the feeding pipe located above the disk on its periphery.
The disk rotation axis may coincide with cavity rotation axis, and the disk has the same drive as the rotating body. The disk rotation axis may coincide with cavity rotation axis, and the disk has an independent drive. Two or more outlet or feeding pipes may be uniformly arranged above the surface of the disk near its periphery along the its circumference length. The feeder may consist of a rotating flat ring and a pipe for feeding powder to this ring, the ring being disposed inside the cavity of the rotating body in the plane perpendicular to the rotation axis of the cavity, and the rotation axis of the ring coincides with the rotation axis of the cavity, the outlet of the feeding pipe being located above the plane of the ring. At least two such flat rings may be located one above another. At least one such flat ring may be located above the flat disk.
The disk rotation axis may not coincide with the cavity rotation rate, the disk having an independent drive, and there is one outlet of the feeding pipe above its periphery. Two or more the disks may be uniformly arranged along the cavity surface. The disks may be arranged at various heights with respect to the lower edge of the cavity surface. The feeder may consist of a rotating disk and a pipe for feeding powder to this disk, the disk being disposed inside the cavity of the rotating body, and the rotation axis of the disk does not coincide with the rotation axis of the cavity and is not parallel to it, the angle between the rotation plane of the disk and the rotation axis of the cavity being within the interval from approximately 45xc2x0 to 90xc2x0, and the disk has an independent drive, and there is one outlet of the feeding pipe over its periphery.
Moreover, two or more disks may be uniformly arranged along the cavity surface. The feeder may represent a feeding pipe with an outlet fitted with a nozzle feeding powder to the feeding zone. Two or more nozzles may be uniformly arranged along the cavity surface. The feeder may comprise a feeding pipe and a conveyer arranged in the cavity of the rotating body so that the powder on the converer moves along the straight line connecting the rotation axis of the rotating body with the cavity surface, and the outlet of the feeding pipe is located above the conveyer near its end which is nearer to the rotation axis. The plane of powder motion on the conveyor may be perpendicular to the rotation axis of the cavity. The angle between the plane of powder motion on the conveyer and the rotation axis of the cavity may be within the range of approximately 45xc2x0 to 90xc2x0. The space in front of the discharge device in the sense of rotation may be surrounded along the entire length of the discharge device by a shell-powder concentrator, which does not adjoin the cavity surface.
The discharge device may represent at least one flexible elastic strip adjoining the cavity surface with the end face of its longer side and arranged along the entire length of the generatrix of the surface of revolution at an angle from approximately 0xc2x0 to 30xc2x0 to the latter. The discharge device may represent at least one flat brush arranged along the entire length of the generatrix of the surface of revolution at an angle from approximately 0xc2x0 to 30xc2x0 to the generatrix. Several the brushes may be assembled into a battery and arranged parallel to one another with an interval equal or exceeding the width of one brush. The discharge device may represent at least one rotating circular brush having an independent drive and arranged along the entire length of the generatrix of the surface of revolution at an angle to the generatrix. The angle may be within the interval from approximately 0xc2x0 to xc2x130xc2x0. The discharge device may represent a conveyer (belt, apron or flight conveyor) with external surfaces of conveying planes made in the form of a brush, which is arranged along the entire length of the generatrix of the surface of revolution. The separator may be fitted with an additional rotating disk whose rotating axis coincides with the rotation axis of the cavity and which is located under the lower level of the surface of revolution.
According to another aspect of the invention, there is provided a system for the dry separation of powders into at least two fractions including a powder to be separated and a separator comprising, a hollow body rotating about a vertical axis, the cavity of the body being open from above and from below and the surface of the cavity representing a surface of revolution with the central axis coinciding with the rotation axis of the body, the upper edge of the cavity having a greater diameter than its lower edge, a system controlling the rotation of the body, at least one feeder continuously feeding dry powder into a feeding zone adjacent to the cavity surface near its lower edge, the length of the zone being at least an order of magnitude less than the circumference of the cavity surface in its lower portion, at least one discharge device continuously removing powder from the cavity surface, which represents an air suction nozzle arranged along the entiro generatrix of the surface of revolution, and at least two hoppers, one of which is intended for powder fraction consisting of powder particles passing over the upper edge of the cavity surface in the course of separation, and the second is intended for powder fraction remaining on the cavity surface until it is sucked in by the nozzle.
According to another aspect of the invention, there is provided a system for dry separation of powders into at least two fractions including a powder to be separated and a separator comprising, a hollow body rotating about an axis and defining a cavity having a powder engaging surface, the surface of the cavity being a surface of revolution which rotates about the axis, an upper edge of the cavity having a greater diameter than a lower edge, a system controlling the rotation of the body, at least one feeder continuously feeding dry powder into a feeding zone adjacent to the cavity surface near the lower edge, the length of the feeding zone being at least an order of magnitude less than a circumference of the cavity surface of the lower edge, at least one discharge device continuously discharging the powder from the cavity surface, the at least one discharge device comprising a body arranged along substantially the entire length of the generatrix of the cavity surface and located immediately in front of the feeding zone aligned with the rotation of the cavity surface, a first hopper for collecting a powder fraction consisting of powder particles passing over the upper edge of the cavity surface, and a second hopper for collecting a powder fraction remaining on the cavity surface until the discharge device discharges the remaining powder fraction from the rotating cavity surface into the second hopper.
In some embodiments, the present invention relates to a combination of the separator as disclosed herein, in combination with a mixture of dry powders to be separated.
The invention provides system for dry separation of powders into at least two fractions comprising:
a) a hollow body rotatable about a vertical axis of rotation, the body having a cavity defined by a surface having an axis of rotation having a central axis coinciding with the axis of rotation of the hollow body, the surface defining the cavity having an upper edge having a greater diameter than a lower edge of the surface defining the cavity;
b) a system controlling the rotation of the body;
c) at least one feeder constructed and arranged to substantially continuously feed dry powder into a feeding zone adjacent to the cavity surface near its lower edge, the length of the zone being at least an order of magnitude less than the circumference of the cavity surface in its lower portion;
d) at least one discharge device constructed and arranged to substantially continuously remove powder from the cavity surface,
e) at least two hoppers, one of which is constructed and arranged to receive a powder fraction comprising powder particles passing over the upper edge of the cavity surface in the course of separation, and the second of which is constructed and arranged to receive a powder fraction remaining on the cavity surface essentially until the discharging device removes it from the rotating surface into the hopper.
The discharge device can comprise an enlongated body arranged along a length of the generatrix of the surface defining the cavity and located immediately in front of the feeding zone.
The slope of the generatrix of the surface defining the cavity with respect to the vertical may be within the limits from about 10xc2x0 to about 45xc2x0 and the roughness of the cavity surface is within about 00.1d to about 0.2d, where d is the diameter of particles, by which the powder is separated into fractions so that particles with diameters dixe2x89xa6d are found in one fraction, and particles with diameter dixe2x89xa7dxe2x80x94in another.
In some embodiments, n pairs feeder/discharging device are uniformly arranged over the cavity surface so that the following relationship is valid: Lxe2x89xa7n(1f+1s+1u), where L is the circumference length of the lower edge of the surface, 1f is the feeding zone length, 1s is the separation zone length, 1u is the unloading zone length, the separation zone length being 1sxe2x89xa71gxc3x97/Vg, where 1g is the distance between the lower edge of the feed zone to the upper edge of the cavity surface, V Is the linear velocity of the upper edge of cavity surface, Vg is the mean velocity of the rise of coarse powder fraction particles along the genratrix of the surface of revolution.
In some embodiments, the feeder comprises a rotating disk and a pipe for feeding powder to the disk, the disk being disposed inside the cavity of the rotating body in a plane perpendicular to the rotation axis of the rotating body, and the outlet of the feeding pipe located above the disk on its periphery.
In some embodiments a disk rotation axis coincides with rotation axis of the surface defining the cavity, and the disk has the same drive as the rotating body.
In some embodiments, a disk rotation axis coincides with surface defining the cavity, and the disk has an independent drive.
In some embodiments, two or more outlets of feeding pipes are uniformly arranged above a surface of the disk near its periphery along the its circumference length.
In some embodiments, the feeder comprises a rotating flat ring and a pipe for feeding powder to this ring, the ring being disposed inside the cavity of the rotating body in the plane perpendicular to the rotation axis of the cavity, and the rotation axis of the ring coincides with the rotation axis of the cavity, the outlet of the feeding pipe being located above the plane of the ring.
In some embodiments at least two flat rings are located one above another. At least one such flat ring may be located above the flat disk.
In some embodiments, the disk rotation axis does not coincide with the cavity rotation rate, the disk having an independent drive, and there is one outlet of the feeding pipe above its periphery.
In some embodiments two or more disks are uniformly arranged along a cavity surface.
The disks may be arranged at various heights with respect to the lower edge of the cavity surface.
The feeder may comprise a rotating disk and a pipe for feeding powder to the disk, the disk being disposed inside the cavity of the rotating body, and the rotation axis of the disk does not coincide with the rotation axis of the cavity and is not parallel to it, the angle between the rotation plane of the disk and the rotation axis of the cavity being within the interval from about 45xc2x0 to about 90xc2x0, and the disk has an independent drive, and the feeding pipe comprises outlet.
Two or more disks may be uniformly arranged along a cavity surface.
The feeder may comprise feeding pipe with an outlet fitted with a nozzle feeding powder to the feeding zone.
Two or more nozzles may be uniformly arranged along the cavity surface.
The feeder may comprise a feeding pipe and a conveyer arranged in the cavity of the rotating body so that the powder on the conveyer moves along the straight line connecting the rotation axis of the rotating body with the cavity surface, and the outlet of the feeding pipe is located above the conveyer near its end which is nearer to the rotation axis.
The powder may be caused to move in a plane of powder motion on the conveyor is perpendicular to the rotation axis of the cavity.
The angle between the plane of powder motion on the conveyer and the axis of rotation of the cavity may be within a range from about 45xc2x0 to about 90xc2x0.
In some embodiments, a space in front of the discharge device with respect to a direction of relative rotation is surrounded substantially along the entire length of the discharge device by a shell/powder concentrator, which does not adjoin the cavity surface.
The discharge device may comprise at least one flexible elastic strip adjoining the cavity surface with the end face of its longer side and arranged along the entire length of the generatrix of the surface of revolution at an angle form about 0xc2x0 to about 30xc2x0 (to the generatrix).
The discharge device may comprise at least one flat brush arranged along the entire length of the generatrix of the surface of revolution at an angle from 0xc2x0 to 30xc2x0 to the generatrix. The brushes may be assembled into a battery and arranged parallel to one another with an interval equal or exceeding the width of one brush.
The discharge device may comprise at least one rotating circular brush having an independent drive and arranged along the entire length of the generatrix of the surface of revolution at an angle to the generatrix and the angle is within the interval from about 0xc2x0 to xc2x1 about 30xc2x0.
The discharge device can comprise a member selected from a conveyer, a belt, an apron or flight conveyer or combinations thereof comprising external surfaces of conveying planes in the form of a brush, which is arranged along essentially the entire length of the generatrix of the surface of revolution.
The separator can comprise a rotating disk whose rotating axis coincides with the rotation axis of the surface defining the cavity and which is located under the lower level of the surface of revolution.
The invention also provides a system for dry separation of powders into at least two fractions including a powder to be separated and a separator comprising:
a) a hollow body rotatable about a vertical axis, the hollow body having a cavity of open from above and from below and the cavity comprising a surface of revolution having a central axis coinciding with the rotation axis of the body, the upper edge of the cavity having a greater diameter than its lower edge.
b) a system rotating the body;
c) at least one feeder continuously feeding dry powder into a feeding zone adjacent to the cavity surface near its lower edge, the length of the zone being at least an order of magnitude less than a circumference of the cavity surface in its lower portion;
d) at least one discharge device constructed and arranged to essentially continuously remove powder from a cavity surface, comprising a suction nozzle arranged along essentially the entire generatrix of the surface of revolution;
e) at least two hoppers, one of which is constructed and arranged to receive a powder fraction comprising powder particles passing over the upper edge of the cavity surface in the course of separation, and the second is intended for powder fraction remaining on the cavity surface until being suctioned by the nozzle.
In other embodiments, the invention provides a system for dry separation of powders into at least two fractions including the system comprising a powder to be separated and a separator comprising:
a hollow body rotating about an axis and defining a cavity having a powder engaging surface, the surface of the cavity being a surface of revolution which rotates about the axis, an upper edge of the cavity having a greater diameter than a lower edge;
a system controlling the rotation of the body;
at least one feeder continuously feeding dry powder into a feeding zone adjacent to the cavity surface near the lower edge, the length of the feeding zone being at least an order of magnitude less than a circumference of the cavity surface of the lower edge;
at least one discharge device continuously discharging the powder from the cavity surface, the at least one discharge device comprising a body arranged along substantially the entire length of the generatrix of the cavity surface and located immediately in front of the feeding zone aligned with the rotation of the cavity surface;
a first hopper for collecting a powder fraction consisting of powder particles passing over the upper edge of the cavity surface;
a second hopper for collecting a powder fraction remaining on the cavity surface until the discharge device discharges the remaining powder fraction from the rotating cavity surface into second hopper.